Motorcycle battery care, Part 2

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Yamaha Motorcycles Street Event - Skagit Powersports


Motorcycle Battery Care

Part 2

By David L. Hough

Smart Chargers

Today’s “smart” battery chargers do a lot more than charge. They read the type of battery, determine its state of charge and condition, and automatically adjust the voltage, current, and charging time it needs to bring it back to health. For a discharged battery, the complex charging algorithm first provides a constant (bulk) charge until voltage spikes at a cut-off point (which varies depending on the battery type). For an AGM, the cut-off voltage might be around 16.0V. For a gel, its maybe 15.0V, and for an FLA, perhaps 14.0V. Then the voltage is reduced and the charge rate (amperage) is tapered off during what is called the “absorption stage,” which may last 4 or 5 hours. The charger then applies a low amperage “float” charge at say, 13.5V.

Some smart chargers periodically shut off for about 30 minutes to check the battery’s self-discharge rate, then turn back on in “float” mode, adjusting the charging voltage and current as needed to maintain the battery at full charge.

The more complex (and more expensive) chargers have algorithms that adjust voltage and amperage continuously. The cheaper chargers just turn on and off in pulses, or perhaps shut off for an hour or two and then turn on when voltage drops to the set limit.

Even with a simpler, cheaper automatic charger, you can just connect it to whatever battery you have, and let it do its thing. Well, let’s throw in the caveats that the charger needs to be producing the correct voltages if it’s to maintain the battery at 90% or 100% of full charge, and that charging voltage is temperature sensitive.

Temperature Affects Charging

A fully-charged battery will survive freezing temperatures, but dies quickly in very hot temperatures. The ideal charging and float voltages can be 2 volts different for cold vs. hot charging. In a hot climate you don’t want a charger that kicks out a voltage that’s too high. Some bikes have voltage regulators set for average temperatures, and they will consistently overcharge batteries in hot climates. We’re lucky here in the Northwest because our typical temperatures are mild enough for batteries to survive for many years. During the scorching summertime, my friends in Texas and Arizona can use the cheap chargers producing lower float voltages that are less likely to overcharge their batteries, but the same chargers will undercharge during the winter.

Ideally, both battery chargers and bike voltage regulators should have temperature compensation, but that adds considerably to the price. A cheap way for manufacturers to deal with the temperature issue is to build regulators with lower voltage limits (favorable to very hot climates), knowing the system will be unable to bring a battery to full charge in a cooler climate. After all, if the battery fails prematurely, that’s the owner’s responsibility.

When you’re buying a battery charger, temperature compensation is a valuable feature, and worth the additional expense. The ideal voltages are quite different for different temperatures. For a gel battery, the ideal charge voltages should be about 0.5V lower, but the float voltages would be the same as for an AGM.

AGM ideal charge and float voltages at various temperatures:

Temperature charge voltage float voltage

0F – 30F 15.10 – 15.40 14.20 – 14.50

40F - 50F 14.80 – 15.10 13.90 – 14.20

60F - 70F 14.45 – 14.75 13.55 – 13.85

90F - 100F 14.00 – 14.30 13.10 – 13.40

110F - 120F 13.80 – 14.10 12.90 – 13.20

You don’t have to remove a battery from the machine to charge it, nor is there any particular advantage to storing a battery in a warm place. The best way to prolong the life of a battery is to keep it charged. If you don’t have an easy way to charge an AGM or gel battery, disconnect it. A well charged AGM should hold a full charge for two months if there are no parasitic loads drawing it down.


On all my machines I have one or more “hot battery” pigtails hanging down in accessible locations. I can plug in a charger, or use the pigtail for powering an electric vest, GPS, or air pump. For any machine with Can Bus electrics, it’s best to wire the pigtail directly to the battery to avoid disrupting or confusing the complex electronics. If you want to install additional electrical equipment bypassing the existing bike circuits, you can add a small fuse panel powered from the battery positive terminal, and feed the charger pigtail from one of the fuses.

On each of my motorcycles I have installed one or more pigtails wired directly to the battery. I can easily plug in a charger, or use the pigtail to connect accessories such as an electric vest or GPS. The circuit stays “hot” even when the ignition is off. This is an SAE plug, available from auto parts stores.

I suggest standardizing on SAE connectors, which are compact, economical, and polarized. The “hot” side coming from the battery should be the female connector enclosed by the rubber sheath. It’s best to power the pigtail through an inline fuse, to protect against accidental shorts--or bored kids with paper clips.

Some machines have auxiliary electrical outlets installed, but such connectors may be limited in amperage, or may only be active when the key is on. A battery charger circuit must be “hot” even when the main switch is off. Before attempting to connect to a bike’s auxiliary outlet, ensure it is always on, and has sufficient amperage for a charger that may occasionally draw higher current—say when first connected to a partially discharged battery.

Battery Condition

Back in the “good old days” it was common practice to suck up some electrolyte and measure its specific gravity to determine the state of charge. Of course, battery acid can quickly eat holes in skin, clothing, metal, and concrete. Today there are battery testing meters that can quickly read the condition and state of charge of a battery without dipping into the acid. If you’re starting to mistrust a battery, it only takes a few minutes at the dealer to get a reading.

Battery Precautions

A charged battery can be dangerous. First, the process of charging a battery is chemical. Charging creates hydrogen gas, which you may recall was what caused the Hindenburg airship to burst into flames. It’s best not to smoke or wave any source of fire near a battery. And if you hear a hissing sound from a sealed battery, it’s an indication it’s being overcharged. It would be wise to quickly unplug the battery charger, step back a few yards, and let the battery cool down. You’d be smart to figure out why it’s overcharging--before it explodes.

Second, the amperage of a starting battery is sufficient to weld steel. You want to be very careful about preventing any metal from bridging between the positive and negative battery terminals. 12 volts isn’t enough to give you an electric shock. Even if you wet your fingers and touch both terminals, you might feel only a tingle. But a steel wrench inadvertently touched across the terminals will conduct full current, becoming red hot in seconds after you hear the dreaded DZZZZP.

To help prevent such fireworks, the procedure for disconnecting a battery is to remove the ground wire first—the big black wire. Then disconnect the positive connection—the big red wire. That way, if a wrench touching the positive terminal happens to touch the frame, there won’t be any fireworks. When installing a battery, connect the positive terminal first, then the negative.


Battery posts are typically lead, and battery bolts are lead plated. Since lead oxidizes in air, the dull oxide must be scraped off the connecting surfaces to allow a good electrical contact. A thin coat of petroleum jelly or battery terminal grease to the connections helps slow the oxidation.

If you notice white fuzzy stuff around a battery, that’s an indication the acid electrolyte is leaking-- and eating metal. It’s more common with flooded batteries, because the fill caps aren’t exactly liquid tight. Battery cases can crack from impacts or ozone, allowing the acid to weep out. Acid can be neutralized with baking soda, but a leaking battery should immediately be removed from the bike and sealed in a plastic bag. Be sure to wash your hands and motorcycle parts with plenty of soap and water after dealing with any acid spills.

Typically, a flooded battery will have a plastic vent tube connected to the top of the battery to allow excess hydrogen (and acid vapors) to escape. It’s worthwhile to make sure the lower end of the tube extends lower than bike parts such as the centerstand or drive chain. Battery acid will quickly corrode metals. Acid cracks in a drive chain link can cause it to disintegrate.


Over my million-some miles and 45 years of motorcycling, I’ve experienced plenty of battery problems. On several occasions I’ve packed the bike for a trip and then gone out the next morning to find the battery dead. Lots of bikes come with factory voltmeters, but most are only active when the switch is on. Because of both my curiosity and my increasingly creaky memory, I installed a Kisan ChargeGuard battery monitoring meter on Sparky the Spyder.

The ChargeGuard is a very clever little display connected to a shunt on the battery negative terminal. I can select voltage, current flow, or temperature, and it comes on automatically when the ignition is turned on or a charger is connected. It was a bit of a PITA getting the wire bundle stuffed through Sparky’s frame and connected to the battery. But it’s really comforting to walk by the parked machine and see the battery voltage displayed. The Kisan meter seems to be very accurate.

With the ACI charger plugged in, but the engine not running, the Kisan ChargeGuard meter reads 13.6V. With the engine running at road speed, the charging system cranks out around 14.1V on this machine.

Buying a Battery

It used to be that unsealed batteries needed to be picked up in person, to avoid acid spillage during shipment. Typically the battery would be shipped dry charged, that is, electrically charged, but drained of electrolyte. The dealer might provide the electrolyte separately, or fill the battery after the sale. Sealed batteries allow shipment through the mail or by parcel delivery with no additional precautions. That gives you the option of either buying a battery from a nearby dealer, or buying it online.

Before buying a replacement battery, note the number on the old battery. That provides the size, capacity, and terminal locations. It’s important to get the positive and negative terminals on the correct side, because the battery cables on the bike are seldom long enough to reach terminals in the wrong position.

It’s smart to dispose of the old battery promptly. When buying from a local dealer, you can usually leave your old battery for disposal. Or you may be able to drop the old battery at a recycling center or auto parts store. It’s best to not leave old batteries lying around where children or animals could get poisoned or burned by acid.

Future Batteries

Battery engineers are working furiously on batteries that are lighter, more powerful, and longer lasting. One new technology is Lithium Iron. There are now Lithium-Iron motorcycle batteries on the market, notably by Shorai. According to testers, the Shorai Lithium-Iron battery has increased cranking power and lighter weight, although there are characteristics that will be strange to those familiar with lead-acid batteries. For example, it helps to run the headlights for several seconds to prepare a Lithium-Iron battery to start the engine. And, wouldn’t you know it? Lithium-Iron batteries require special chargers. Here we go again!

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